The mandible is connected to the cranium by the temporomandibular joints, located immediately in front of the ears. Rotation of the mandible about these joints is accomplished by the masticatory muscles, each of which extends from an opposite side of the mandible to a connecting point on the cranial bones. The masticatory muscles have an at rest position between their extended and contracted states. Under normal physiological conditions involving the outgrowth of a full complement of teeth, the mandibular portion of each temporomandibular joint will rest lightly in the cranial portion of the joint, and the muscles will be relaxed, or at rest.
Masticatory muscle related stresses and/or pain can arise due to differences in occlusal pressures along the upper and lower dental arches. Temporomandibular joint dysfunction syndrome relates to occlusion-muscle incompatibility. Masticatory muscle accommodation is a key factor in the etiology of this syndrome. Psychological tension and stress can lead to temporomandibular joint dysfunction or bruxism in otherwise stable mouths with normal occlusion.
The most frequent jaw movement involves elevation of the mandible from its rest position into centric occlusion. Simple elevation of the mandible is normally powered almost entirely by the elevator muscles, other muscles providing only a minor bracing action. The bilateral temporals, masseters and medial pterygoids provide an excess supply of elevator motor units. Since these motor units alternate in function, with fatigued units "dropping out" to rest while others take their place, mandible elevation can be continued almost indefinitely without overfatiguing these muscles.
Occlusion-muscle dysfunction alters this condition drastically because accommodation has a highly selective effect on the masticatory muscles, increasing their activity disproportionately in certain areas of the bilateral complex. In the presence of occlusionmuscle disharmony, atraumatic closure into centric occlusion requires that the mandible be adjusted every time it is elevated into occlusion. If, for example, the required adjustment is horizontal, the muscle areas capable of producing such horizontal movements must be called into activity with the same frequency as are the elevator muscle areas Unfortunately, there are far fewer of these horizontal-adjustor motor units than elevator motor units.
Ultimately the functional capacity of these comparatively few horizontal motor units is exceeded, which triggers an exhaustion-incoordination-spasm sequence and development of the temporomandibular joint syndrome symptoms The resulting tenderness and spasm are found most frequently in the lateral pterygoid muscles which function as anterior adjustors of mandibular placement.
In psychological stress related syndromes, the muscles become fatigued as a result of nocturnal clenching or grinding of the teeth. These nocturnal activities give rise to the same symptoms as malocclusion-based temporomandibular joint dysfunction.
The sequence of muscle dysfunction spreads beyond the masticatory muscles, producing an entire constellation of primary symptoms of the temporomandibular joint pain-dysfunction syndrome. These symptoms include pain and/or tenderness in the temporomandibular joint area or masticatory muscles; "clicking" in the temporomandibular joint; limitation of jaw opening; restriction of jaw movement; and secondary symptoms which are medical in nature, being transmitted to other, more distant areas of the head and neck. These secondary symptoms probably include some of the most widespread and problematic conditions medicine has to deal with, namely, headache (including "tension" headaches, which account for 90% of all headache), atypical facial neuralgias, tinnitus, and neck and ear pain, among others. Also, certain neuromuscular disorders of the face, head and neck, shoulders, back, arms and hands can occur. These secondary symptoms are functional disturbances which exhibit no organic changes in the affected tissues, making diagnosis difficult. They are often ill-defined and difficult for the patient to describe.
These symptoms are usually diagnosed as purely medical in nature because they occur at some distance from the teeth. Their masticatory muscle origin unfortunately is not readily apparent. The usual result is that treatment is mistakenly directed to the secondary symptom's locale rather than to the underlying "invisible malocclusion." Such invisible malocclusions are common, but difficult to detect. Intercuspation of the teeth appears normal, while the underlying faulty (accommodation-necessitating) craniomandibular relationship is hidden by the automatic compensatory action of the muscles. The secondary symptoms resulting from temporomandibular joint dysfunction thus are usually treated palliatively instead of having their basic cause eliminated. For malocclusion-based muscle dysfunction definitive therapy is essentially an orthopedic procedure and requires correction of the faulty cranio-mandibular relationship by a dentist. For psychological-stress related dysfunctions, orthopedic procedures are largely unnecessary. In these cases, negative psychological feedback, such as described hereinafter, can be used to interrupt the stress-related grinding or clenching events.
A related condition is known as bruxism. This condition involves abnormal and excessive grinding of the teeth, typically during sleep. This condition has been linked to episodes of emotional stress. Excessive grinding, if unchecked, can lead to malocclusion and result in the occurrence of malocclusion-related temporomandibular joint dysfunction syndrome described above.
Prior art methods of treating temporomandibular joint dysfunction and bruxism involve clinical monitoring devices to measure the amount of pressure being asserted, splints to be worn during sleep to prevent the wearing of teeth, and behavior modification devices wherein an electrical shock is provided to the jaw muscles to interrupt a nocturnal episode without waking the patient. The present invention provides for the first time an intraoral sensing device and therapeutic apparatus which does not require continual clinical monitoring. It is relatively low cost and very simple to use.